After World War II flying clubs rebirth lacked of easy-to-use training aircraft. This problem was recognized by the Department of Civil Aviation. The director, Eng. Konrad Jagoszewski, head of the technical department of the Civil Aviation Department, Eng. Richard Bartel and Eng. Mieczyslaw Pęczalski (former deputy director of the PZL) developed a preliminary WTT for such aircraft.
It was agreed that the plane has to be a two-seater with side by side. The project was to be powered by a Czech Walter Mikron III 65 hp.
In 1946 the order went to the Experimental Aviation Workshops (LWD) in Lodz, where a group of designers headed Eng. Tadeusz Sołtyk could immediately proceed with the task. It was a light low-wing cantilever monoplane of a mixed construction, with a crew of two, sitting side by side, and fixed conventional landing gear. The plane was named Zak (old-fashioned "student"), and later added digital designation Zak-1. The prototype first flight performed on 23.03.1947 and received the registration SP-AAC, becoming the fourth post-war Polish plane (Starling-2, PZL S-1, Starling-3).
Zak-1 had a few glitches, among other things, they were improperly routed links the elevator, causing the looping out. They also changed the balance of the aircraft. Also, the engine had a tendency to overheat. The oil tank was changed to one that had a greater surface area, which solved the problem partially. Also, there were problems with feeding fuel to the engine. At certain points the motor is not getting fuel and choking. The problem was caused by the collection box intermediate (outgoing). They reported comments to the windshield and canopy.
The Zak-1 was good in flight. In flight at low speed there was warning vibration in the control stick. It was difficult to enter a spin, and recovery was easy. During 1947-1948. plane made dozens of propaganda flights.
Approval for the Zak-1 was received in February 1949. The aircraft rated positively, but acrobatics wer not allowed. The reason was the weak power unit. During the performance figures pilot pilot lost directional steering. The result was that at the exit of the loop faced sideways with loss of height. They tried to remedy this by increasing the height of the vertical tail.
Even before the first flight the Walter Mikron III was tested on a dynamometer. Instead of 65 hp, it only had 56 hp, forcing manufacturers to seek alternative propulsion.
With testing of the Zak-1 not yet completed, the Zak-2 construction was started. It was designed for installation of the Polish WN-1 motor (named constructor W. Narkiewicz), sometimes labeled PZL A-65. Since the WN-1 was in a trial phase, a Continental A-65 was used. The engine was removed from a Piper L-4. The Zak-2 plane did not differ much from the first prototype. Initially, it had mechanical brakes, which were later replaced by more effective hydraulic. It also had an oen cabin, equipped only with a windshield. Zak-2 was flown on November 27, 1947 and received registration SP-AAE. The aircraft underwent a trial approval in the autumn of 1951.
Positive Rating for the Zak-1 prompted the ministry to purchase 10 machines for flying clubs. The design appeared successful and the Ministry of Communication ordered a series of 10 aircraft. They were to be powered by licence-built A-65 engines, but since plans of engine production were abandoned, it was decided to fit them with Walter Mikron engines. They were also fitted with a closed canopy, sliding rearwards, and named Żak-3.
The design of the airplane Zak was threatened after work was suspended on the Polish WN-1 motor. Walter has not signed a contract for the production of the Walter Mikron III engines in Poland and it was decided to purchase a number of engines directly from Czechoslovakia.
The construction of the aircraft was carried out in the hall on the first floor of the main production building in Lodz. Completed aircraft, engines and painted, were drawn through a window on a makeshift wooden ramp (ramp) and slides to the ground. Wings also followed this path. The company which supplied the engines to Lodz, allegedly had the wrong address. In fact, they could not find the the street, because at that time the Communists gave many streets new names.
Ten planes were built by the LWD in the end of 1948, the first of them, SP-AAS, was flown on November 8, 1948. They had markings: SP-AAS to SP-AAZ, and SP-BAA to SP-BAC. At least one (SP-AAX) had engine replaced later with 85 hp (63 kW) Cirrus F.III.
The 10 aircraft machines were built two weeks before the deadline, although in fact only three of them had their first flight. In addition, the team realized that the machines may have shortcomings resulting from the rush and very nervous atmosphere. Fortunately, these defects have been timely detected and removed, even before the first flights, after the unification congress of communists.
Eng. Tadeusz Soltyka realized that the engines were weak and had a tendency to overheat. The Zak-3 SP-AAX underwent an examination at the Central Institute of Aviation in Warsaw and received the same assessment as Zak-1. The designers are still working to eliminate engine overheating. The focus is on different types of bottom oil tank; Additional ribs, ribs pressed, an additional barrier inhibiting mixing of oil was most effective.
Zak-3 SP-AAS, SP-AAT, SP-BAB, for a time were used in LWD to the various tests. For example, you try to use different profiles of wings, but without great effect. They also tested new hydraulic brakes.
Zak-3 SP-AAX on air exhibition in Wroclaw was equipped with a Cirrus III RWD-21 engine. However, in this arrangement, the plane never flown. The aircraft was painted the color of the sea (top) and blue-silver (bottom).
10 LWD Zak-3 during the celebration of their transfer on 1.12.1948. These
aircraft are painted in red (hulls and vertical tail) and silver (wings). Registration
marks on the hull of silver, and red on the wings.
They were operated in aero clubs Kujawski, Poznan, Krakow, Gdansk, Bielsko-Biała and Warsaw. They were used in the Polish regional aero clubs until 1955.
On October 20, 1948 there was flown a prototype of the last variant, Żak-4, meant for a glider towing. It had a 105 hp Walter engine and an open canopy. Once the plane had to make an emergency landing. Attempts were made towing gliders; Zak-4 with a glider Hedgehog need 215-340 m run. Zak-4 with a glider Vulture need to 400-500 m, while Po-2 glider Vulture need 250 m. Since it showed unsuitable for glider towing, the Żak-4 was not built in series, and the prototype was re-fitted with a closed canopy and used as a touring plane in aero club (markings SP-BAE).Due to the much more powerful engine, it towered over the Zak-3 machines.
In December 1963 Żak-3 SP-AAX was transferred to the Air and Space Museum in Krakow. It is preserved in the Polish Aviation Museum in Kraków (disassembled as for 2007)
The first prototype powered by Walter Mikron III engine.
The second prototype without canopy and powered by Continental A-65 engine.
Main production version with closed canopy and powered by Walter Mikron III engine, 10 built.
Prototype of the glider towing version with open canopy (later refitted with a closed one) and powered by Walter engine.
Engine: 1 × Walter Mikron III, 65 hp (48 kW)
Length: 7.6 m (23 ft 11 in)
Wingspan: 11.8 m (38 ft 8½ in)
Height: 1.95 m (6 ft 5 in)
Wing area: 17 m² (183 sq ft)
Empty weight: 400 kg (880 lb)
Loaded weight: 620 kg (1,365 lb)
Maximum speed: 160 km/h (86 knots, 99 mph)
Range: 400 km (216 nmi, 248 mi)
Service ceiling: 3,500 m (11,500 ft)
Rate of climb: 2.7 m/s (520 ft/min)